The present invention relates to a refrigerant cycle apparatus in which a multistage compression type compressor constitutes a refrigerant circuit including an electromotive element and first and second compression elements driven by the electromotive element in an airtight container to suck an intermediate-pressure refrigerant gas compressed by the first compression element into the second compression element and to compress and discharge the gas.
For example, a two-stage compression type rotary compressor has heretofore comprised an electromotive element including a stator and rotor (the number of revolutions are controlled by an inverter), a first rotary compression element driven by the electromotive element, and a second rotary compression element attached via a phase difference of 180 degrees, which are stored in an airtight container (see Japanese Patent Application Laid-Open No. 2-294587, for example).
Moreover, a refrigerant gas is sucked on a low-pressure chamber side of a cylinder via a suction port of the first rotary compression element by rotation of the electromotive element, and compressed to have an intermediate pressure by operation of a roller and vane. The gas is discharged, for example, into the airtight container from a high-pressure chamber side of the cylinder via a discharge port, discharge noise silencing chamber, and intermediate discharge tube.
The intermediate-pressure refrigerant gas discharged into the airtight container is sucked on the low-pressure chamber side of the cylinder of the second rotary compression element, and compressed by the operation of the roller and vane to constitute a refrigerant gas at a high temperature/pressure. The gas flows into a gas cooler constituting a refrigerant circuit from the high-pressure chamber side via the discharge port and discharge noise silencing chamber, is air-cooled by an outside air, thereafter pressed by an expansion valve (decompression device), and supplied to an evaporator. Then, the refrigerant evaporates, then absorbs heat from periphery to fulfill a cooling function, and controls air in a chamber of a vehicle, for example, in a car air conditioner.
Additionally, when the inside of the chamber of the vehicle is at a high temperature, or when a rotary compressor is restarted in a short time after stopping the vehicle, a refrigerant pressure on the low-pressure side, sucked into the first rotary compression element, sometimes rises. That is, when the compressor is restarted in a short time after the stopping, an amount of refrigerant existing in the evaporator immediately after the stopping is large. Therefore, even when the rotary compressor starts, the refrigerant pressure on the low-pressure side does not easily drop.
On the other hand, the refrigerant pressure on the high-pressure side is controlled not to be raised at a starting time for protection of the refrigerant cycle apparatus. Since the pressure on the high-pressure side is determined at an outside air temperature, a pressure reverse phenomenon occurs at a low outside air temperature. In the phenomenon, a discharge refrigerant pressure of the first rotary compression element becomes higher than that of the second rotary compression element. When this pressure reverse occurs, the rotary compressor falls in an abnormal run state, the operation of the vane becomes unstable, and this causes a problem that durability and run efficiency drop.